Physical properties (chemical adsorption rate, viscoelasticity, thickness, and conformation) for self-assembled monolayers (SAMs) of mercapto oligo (ethylene oxide) methyl ethers on gold were determined by quartz crystal microbalance (QCM). The values of thickness, shear viscosity and elastic shear modulus of SAMs increase with unit number of oligo (ethylene oxide) segment. However, the chemical adsorption rate determined by a Langmuir isotherm does not show such a unit number regularity. Those results suggest that difference in unit number of oligo (ethylene oxide) segment can significantly affects physical properties of SAMs.